Post on 05-Jun-2020
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GMS 10.0 Tutorial
MODFLOW – SFR2 Package The MODFLOW Streamflow-Routing (SFR2) Package Interface in GMS
Objectives Learn how to create a model containing SFR1/SFR- type streams. The tutorial is based on the test
simulations contained in the SFR1 package documentation. Create a conceptual model of the streams
using arcs and orient them from upstream to downstream. Learn about stream segment and reach
numbering. Create a parameter for stream conductance.
Prerequisite Tutorials MODFLOW – Conceptual
Model Approach I
Required Components Map Module
MODFLOW
Time 55-65 minutes
v. 10.0
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1 Introduction ......................................................................................................................... 2 1.1 Outline .......................................................................................................................... 3
2 Stream Package Basics........................................................................................................ 3 2.1 Reaches and Segments ................................................................................................. 3 2.2 Routing ......................................................................................................................... 3
3 Description of Problem ....................................................................................................... 4 4 Getting Started .................................................................................................................... 5 5 Open the Starting Project ................................................................................................... 5
5.1 Save the Project with a New Name .............................................................................. 6 6 Digitize the Stream Arcs ..................................................................................................... 7
6.1 Create a conceptual model ........................................................................................... 7 6.2 Create a coverage ......................................................................................................... 7 6.3 Create the Arcs ............................................................................................................. 7
7 Correct the Arc Directions ................................................................................................. 8 8 Stream Reach and Segment Numbering ............................................................................ 9 9 Assign Arc Attributes ....................................................................................................... 10
9.1 Arc A .......................................................................................................................... 11 9.2 Arc B-H ...................................................................................................................... 12 9.3 Channel Cross Sections .............................................................................................. 14
10 Segment IDs ....................................................................................................................... 14 11 Map MODFLOW ......................................................................................................... 15 12 SFR2 Package Dialog ........................................................................................................ 15 13 Save the Project and Run MODFLOW .......................................................................... 16 14 Compare the Solutions ...................................................................................................... 17 15 Animation .......................................................................................................................... 18 16 Flow Budget ....................................................................................................................... 18 17 Creating an SFR Parameter ............................................................................................. 20 18 Saving and Running MODFLOW ................................................................................... 21 19 Conclusion.......................................................................................................................... 21
1 Introduction
The MODFLOW SFR2 package is used to model streamflow routing and unsaturated
flow beneath streams. It is an evolution of the SFR1 package, which was derived from
the original MODFLOW stream package, STR1. GMS supports all three stream
packages. The SFR2 package is very similar to the SFR1 package with the main
difference being support for unsaturated flow beneath streams. The SFR2 package can
read files prepared for the SFR1 package.
Because of the grid-independent conceptual model approach that GMS has long
supported, GMS is an ideal modeling interface for creating streams. Stream segments
and reaches must be listed in a particular order that can be quite tricky to get right if
preparing a file by hand. GMS takes care of stream ordering automatically so the user
never has to worry about it. The simple point-and-click interface makes it very easy and
intuitive to create streams in GMS.
This tutorial illustrates how to create a model containing SFR1/SFR2 type streams. The
tutorial is based on the test simulations contained in the “MODFLOW SFR1 Package”
documentation.
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1.1 Outline
Here are the steps in this tutorial:
1. Open a GMS project.
2. Add stream feature arcs by digitizing a background image.
3. Ensure that the stream arcs are pointing in the right direction.
4. Assign attributes to the stream arcs.
5. Save and run the model.
6. Examine the solution.
2 Stream Package Basics
2.1 Reaches and Segments
The SFR2 package divides streams into reaches and segments.
A stream reach is a section of a stream that is associated with a
particular finite-difference cell used to model ground-water flow and
transport. A segment is a group of reaches that have (1) uniform rates of
overland flow and precipitation to them; (2) uniform rates of
evapotranspiration from them; (3) uniform or linearly changing
properties (for example; streambed elevation, thickness, and hydraulic
conductivity, and stream depth and width); (4) tributary flows or
specified inflow or outflow (only in the first reach); and (5) diversions
(only from the last reach). (Prudic, et. al., 2004:2)
In GMS, a stream segment corresponds to a single arc. A stream reach doesn’t have a
corresponding representation in the conceptual model but exists only on the grid cells
after having mapped the conceptual model to the grid.
2.2 Routing
In addition to tracking flow between streams and the underlying aquifer, the MODFLOW
stream packages (STR1, SFR1 and SFR2) also route the flow of water through a stream
network. The stream network can include tributaries, diversions, and lakes (in
conjunction with the Lake package).
Routing is accomplished by determining the inflows for a reach (which are specified for
the most upstream reach), adding or subtracting leakage to the aquifer, and allowing any
remainder to pass to the next downstream reach as inflow. The process is repeated for the
next downstream reach and so forth.
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This is different from the MODFLOW River package which only tracks flow between
the river and the aquifer. With rivers, once water has entered the river, it is lost to the
model, whereas, with the stream packages, that water can travel downstream and
possibly reenter the aquifer at another point.
Also unlike the River package, the water depth is not specified in the stream packages
but is calculated based on the flow. There are several different options available for
calculating water depth, including using Manning’s equation or a depth vs. flow table.
3 Description of Problem
The model in this tutorial is from the SFR1 documentation “A New Streamflow-Routing
(SFR1) Package to Simulate Stream-Aquifer Interaction With MODFLOW–2000” by
David E. Prudic, Leonard F. Konikow, and Edward R. Banta, U.S. Geological Survey
Open-File Report 2004-1042. The model is illustrated in Figure 1. The problem is a
hypothetical one “developed for an alluvial basin in a semiarid region in which recharge
to the aquifer is primarily leakage from streams that enter the basin from mountains on
the northwest, northeast, and southeast” (Prudic, et al., 2004:13). One grid layer is used.
Figure 1 An SFR1 stream network. (Prudic, et al., 2004)
The simulation has two stress periods. In the first stress period, the wells in the middle of
the model extract water from the model and draw down the water table. In the second
stress period, the wells are turned off and the head recovers from the draw down. The
stream data is held constant for both stress periods.
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4 Getting Started
Do the following to get started:
1. If necessary, launch GMS.
2. If GMS is already running, select the File | New command to ensure that the
program settings are restored to their default state.
5 Open the Starting Project
The point of this tutorial is to illustrate the SFR2 package, so this tutorial won’t spend
time entering in all the other MODFLOW inputs. The user will just read them in from
files that have already been created.
1. Select the Open button.
2. Locate and open the Tutorials\MODFLOW\sfr2 directory.
3. Select the file entitled "start.gpr."
4. Click Open.
The user should see a figure showing a grid with some streams and contour lines as
shown in Figure 2. This figure comes from the MODFLOW SFR1 documentation.
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Figure 2 Background image in GMS, taken from the MODFLOW SFR2 documentation
Notice the Project Explorer includes a 3D grid and a MODFLOW simulation (the user
may need to expand items in the Project Explorer to see the MODFLOW simulation).
Figure 3 Project Explorer contents for the beginning project
5.1 Save the Project with a New Name
Now save the project with a new name.
1. Select the File | Save As menu command.
2. Change the File name to "SFR2_GMS."
3. Click Save.
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The user may wish to select the Save button occasionally to save the work as the user
continues with the tutorial.
6 Digitize the Stream Arcs
In GMS, it is only possible to create streams by using the conceptual model approach.
That is, the user must use feature objects and map them to the grid. The user cannot
create streams directly on the grid.
The user will create the stream arcs by digitizing the background image.
6.1 Create a conceptual model
First, it is necessary to create a MODFLOW conceptual model.
1. In the Project Explorer, right-click somewhere in a blank area and select the New
| Conceptual Model command from the pop-up menu.
2. In the Conceptual Model Properties dialog, change the Name to "Test 1."
3. Click OK.
6.2 Create a coverage
1. Right-click on the "Test 1" conceptual model and select the New Coverage
menu command from the pop-up menu.
2. In the Coverage Setup dialog, change the Coverage name to "Streams."
3. In the list of Sources/Sinks/BCs on the left, turn on the Stream (SFR2) option.
4. Change the Default elevation to "1500" so the coverage will be above the grid.
5. Click OK.
6.3 Create the Arcs
Now the user will create the arcs.
1. Select the Create Arc tool.
2. Create arcs by clicking on and following the blue lines in the figure. These are
labeled “Green Creek,” “Ditch,” “Little Creek,” and “Blue River.” The arcs
should be located approximately as shown in Figure 4.
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Figure 4 Location of stream arcs after digitizing
Now that the arcs have been digitized, the user no longer needs the background image.
3. In the Project Explorer, turn off the “GIS Layers” folder.
7 Correct the Arc Directions
Arcs have a direction associated with them. The direction is from the starting node to the
ending node and is defined when the user first creates the arc. Usually the direction
doesn’t matter, but with streams it does. It is necessary to make sure that the arcs go from
upstream to downstream. The direction can be displayed and reversed if needed.
The user must now check the arc direction and make sure all the arcs are pointing from
upstream to downstream.
1. Click the Display Options button.
2. In the Display Options dialog, make sure Map Data is selected in the list on
the left.
3. Turn on the Arc direction arrows option.
4. Click OK.
The user should now see arrows on the arcs. The arrows should be pointing as shown in
Figure 5. If any of the arcs are pointing in the wrong direction, do the following:
5. Switch to the Select Arcs tool.
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6. Right-click on an arc that is pointing the wrong way (if there are any) and select
the Reverse Arc Direction command from the pop-up menu. Repeat for all arcs
which point the wrong direction.
Figure 5 Arc directions
All the arcs should now be pointing the correct direction, matching Figure 5. Now it is
necessary to turn the arrows back off.
7. Click the Display Options button.
8. In the Display Options dialog, make sure Map Data is selected in the list on
the left.
9. Turn off the Arc direction arrows option.
10. Click OK.
8 Stream Reach and Segment Numbering
With GMS, the user generally won’t need to worry about stream segment and reach
numbering because GMS figures it all out automatically. However, it is a concept the
user should be aware of; moreover, the user will see the numbering in the SFR2 package
dialog, which is covered later in this tutorial.
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According to the SFR1 package documentation, “The numbering of segments and
reaches is important. Segments are numbered sequentially from the farthest upstream
segment to the last downstream segment … Reaches within a segment must be numbered
sequentially from the farthest upstream reach in a segment to the last downstream reach”
(Prudic, et al., 2004:3). Figure 6 illustrates stream and segment numbering.
Figure 6 Illustration of stream segment and reach numbering. (Prudic, et al., 2004)
GMS assigns an integer ID number to each arc automatically as it is created. This ID
number is NOT the stream segment number. Stream segment and reach numbers are only
determined when the Map MODFLOW command is executed. The user should be
careful not to confuse arc ID numbers with stream segment numbers.
9 Assign Arc Attributes
Now the user will assign the stream attributes to the arcs.
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Figure 7 Arcs with letters to distinguish them
9.1 Arc A
1. With the Select Arcs tool still active, double-click on arc A as given in
Figure 7. This brings up the Attribute Table dialog.
2. Change the Type to “stream (SFR2).”
3. Enter the remaining values as given in the following table (only the columns
with changes are shown):
ICALC FLOW HCOND1 THICKM1 ELEVUP HCOND2 THICKM2 ELEVDN
table (4) 25 .00003 3 1095 .00003 3 1075
There are a lot of columns in the dialog so the user will need to scroll to the right to see
everything. The user can also stretch the dialog to make it bigger.
4. Scroll to the far right and click on the … button in the Flow Table column.
5. In the Stream Flow Table dialog, enter the following table of information:
B
A
C
D
F
E
G
H
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Flow Depth Width
.5 .25 3
1 .4 3.5
2 .55 4.2
4 .7 5.3
7 .8 7
10 .9 8.5
20 1.1 12
30 1.25 14
50 1.4 17
75 1.7 20
100 2.6 22
6. When the data has been entered, click OK to close the Stream Flow Table
dialog.
7. Click OK to close the Attribute Table dialog.
9.2 Arc B-H
1. Repeat the above procedure to assign the appropriate values to arcs B through H
in Figure 7. Refer to the values shown in Table 1 and Table 2 below.
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ARC Letter
from Figure 7
Type ICALC Diversion FLOW ROUGHCH ROUGHBK CDPTH FDPTH AWDPTH BWDTH
A Stream (SFR2) table (4) 25
B Stream (SFR2) wide channel (1) .03
C Stream (SFR2) specified (0) 10
D Stream (SFR2) wide channel (1) 10 .03
E Stream (SFR2) power function (3) 0.3 0.35 3.8 0.6
F Stream (SFR2) wide channel (1) .03
G Stream (SFR2) cross section (2) 150 .025 .045
H Stream (SFR2) cross section (2) .025 .045
Table 1 Stream arc attributes
ARC
Letter
from
Figure 7
HCOND1 THICKM1 ELEVUP WIDTH1 DEPTH1 HCOND2 THICKM2 ELEVDN WIDTH2 DEPTH2
A .00003 3 1095 .00003 3 1075
B .00003 3 1075 12 .00003 3 1050 12
C .00003 2 1075 10 2 .00003 2 1060 6 1
D .00003 3 1080 10 .00003 3 1060 10
E .00003 3 1060 .00003 3 1045
F .00003 3 1045 12 .00003 3 1025 12
G .00006 3 1040 .00006 3 1025
H .00006 3 1025 .00006 3 990
Table 2 Stream arc attributes continued
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9.3 Channel Cross Sections
Arcs G and H use a cross section to determine the stream depth. The user needs to enter
the cross section points.
1. Double-click on arc G as given in Figure 7.
2. In the Attribute Table dialog, scroll to the right to view the Channel Cross
Section column.
3. Click on the … button in the Channel Cross Section column.
4. Enter the following values in the XY Series Editor:
Distance Elevation
0 20
10 13
80 10
100 2
150 0
170 10
240 13
250 20
5. Click OK to exit the XY Series Editor dialog.
6. Click OK to exit the Attribute Table dialog.
7. Repeat the procedure (steps 1-6) to assign the following cross section to arc H:
Distance Elevation
0 25
10 17
80 13
100 4
150 0
170 10
240 16
250 20
10 Segment IDs
GMS can display the stream segment ID numbers. Now turn them on.
1. Click the Display Options button.
2. In the lower right corner, turn on the Segment ID option.
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3. Click OK to exit the dialog.
The user should notice some numbers displayed in the middle of each arc. They are all 0.
That is because the user has not yet mapped the conceptual model to the grid using the
Map MODFLOW command. Until this is done, GMS does not know how the stream
segments should be numbered. After the Map MODFLOW is done, the stream
segment numbers will follow the rule of upstream to downstream.
11 Map MODFLOW
Everything that was needed has been entered to in the conceptual model and can now be
mapped to the grid.
1. Select the Feature Objects | Map MODFLOW menu command.
2. Click OK.
Notice the stream segment numbers are no longer all 0s. The stream segments have been
numbered so that downstream numbers are always greater than upstream numbers.
12 SFR2 Package Dialog
Now the streams in the conceptual model have been mapped to the grid. The
MODFLOW Stream (SFR2) Package dialog shows all of the stream segments and
reaches on the grid.
1. In the Project Explorer, click on the “3D Grid Data” item.
2. Select the MODFLOW | Optional Packages | Stream (SFR2) Package menu
command.
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Figure 8 MODFLOW Stream (SFR2) Package dialog
The stream segments are listed in the top spreadsheet and the reaches in the bottom
spreadsheet. GMS calculated the reach lengths (RCHLEN) during the Map
MODFLOW process.
Notice that, in this dialog, the user can edit most things but not the segment numbers
(NSEG), the cells that the reaches are in (cell ID), or the ISEG or IREACH numbers. Nor
can segments or reaches be added. Thus, the user can only create stream data by mapping
to MODFLOW from a conceptual model. If the user reads in a MODFLOW simulation
with SFR2 data, it will populate the stream package dialog even if the user doesn’t have
a conceptual model.
3. Click OK to exit the dialog.
13 Save the Project and Run MODFLOW
The next step is to save the project.
1. Select the Save button.
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2. Select the MODFLOW | Run MODFLOW menu command.
3. After the model finishes, select the Close button.
The solution is imported and displayed as contours.
14 Compare the Solutions
Compare the new solution with the original one from the USGS.
1. Select the Contour Options button.
2. Change the options to match the figure below.
Figure 9 Contour Options dialog
3. Click OK to exit the dialog.
4. In the Project Explorer, turn on the” GIS Layers” folder.
Notice how the GMS contours match the contours on the background image pretty
closely. The match isn’t perfect for a couple of reasons. First, the stream input generated
by GMS differs some from the original USGS input. In particular, the reach lengths are
different. The original USGS files, which were built by hand, contain rough estimates for
the length of the stream channel within each model cell. GMS, on the other hand,
calculates this value by intersecting the stream arcs with the grid cells.
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The second reason why the contour lines differ is due to the different methods used by
the USGS and GMS to interpolate and generate contour lines from gridded data.
5. In the Project Explorer, turn off the “GIS Layers” folder.
15 Animation
Since this model is transient, a good way to examine the results is to use an animation.
The user will animate color filled contours.
1. Select the Contour Options button.
2. In the Dataset Contour Options – 3D Grid – Head dialog, switch the Contour
method to “Color Fill.”
3. Click OK.
4. Select the Display | Animate menu command.
5. Accept the defaults and click Next.
6. Again accept the defaults and click Finish.
It will take a minute to generate the animation. After it is finished generating it will play
automatically. The animation clearly shows how the wells draw down the head in the
first stress period and how the head recovers in the second stress period.
7. Feel free to play around with the controls on the animation window.
8. When finished, close the animation window.
16 Flow Budget
Now look at the flow budget for streams.
1. Select the MODFLO W| Flow Budget menu command.
This brings up the Flow Budget dialog. Notice the Streams (SFR2) item. There is more
flow in than out. Thus the streams are mostly losing water—water is flowing from the
streams in to the aquifer in most places. But there is some flow out from the aquifer to
the streams.
2. Click OK.
With other MODFLOW packages, the user can click on a feature object in the map
module and see the flow associated with that object. GMS does this by using the
MODFLOW OBS process. Streams, however, don’t participate in the OBS process, so
this is not available. However, the user can look at the flow on a cell-by-cell basis.
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3. In the Project Explorer, click on the “3D Grid Data” item.
4. Expand the items under the “3D Grid Data” item in the Project Explorer
until the user can see the MODFLOW solution. Expand the solution too.
Figure 10 Project Explorer showing the MODFLOW solution
5. Right-click on the CCF item and select CCF Datasets from the pop-up menu.
6. Select the “Stream Leakage” dataset to make it active.
7. Select the Contour Options button.
8. Switch the Contour method to “Block Fill.”
9. Change the Contour interval to “Number of Contours,” and set the number to 10.
10. Click OK to exit the dialog.
The user should see something like Figure 11 below. With the Select Cells tool, the
user can move the mouse over the grid cells and watch the status bar at the bottom of the
graphics window and see what the stream flow is throughout the grid.
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Figure 11 Block Fill showing stream in/out flow
17 Creating an SFR Parameter
Now the tutorial will illustrate the creation of an SFR parameter. The user will change
the conductance on the first SFR segment at the top-left of the model to use a parameter
instead of specifying the conductance value.
1. Select the “Map Data” folder in the Project Explorer.
2. With the Select Arcs tool, double-click on the top-left arc to open the
Attribute Table dialog.
3. Change the value in the HCOND1 and HCOND2 fields to -10.0.
4. Click OK to exit the dialog.
5. Select the Feature Objects | Map MODFLOW menu command.
6. Click OK.
7. Select the MODFLOW | Parameters command to bring up the Parameters
dialog.
8. Click the Initialize from Model button. Notice that a new parameter has been
created. Change the Value to “0.00003.”
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9. Click OK to exit the Parameters dialog.
10. Select the MODFLOW | Optional Packages | Stream (SFR2) Package menu
command.
This brings up the MODFLOW Stream (SFR2) Package dialog. Notice that the Segments
table now shows Hc1fact and Hc2fact columns at the far right. The values listed in these
columns are multiplied by the parameter value to give the final conductance values for
the SFR boundary condition.
11. Click OK to exit the MODFLOW Stream (SFR2) Package dialog.
18 Saving and Running MODFLOW
Now it is possible to save our changes and run MODFLOW.
1. Select the File | Save As menu command.
2. Change the project name to “SFR2_GMS2.”
3. Select the MODFLOW | Run MODFLOW menu command.
4. After the model finishes, select the Close button.
The user should notice that the new solution is the same as the previous run.
19 Conclusion
This concludes the tutorial. Here are some of the key concepts in this tutorial:
It is possible to use GMS to create MODFLOW models with STR1, SFR1, and
SFR2 type streams.
Streams must be created in the Map module using Feature Objects and cannot be
created directly on the grid.
It is necessary to make sure that the stream arcs are oriented from upstream to
downstream correctly.
The conceptual model does not have to include all aspects of the model. In this
case, the conceptual model contained only the streams and the other boundary
conditions were already part of the grid.
GMS automatically determines the proper ordering of the stream data for input
to MODFLOW based on the orientation and topology of the stream arcs.
Unlike with other MODFLOW packages, with streams, the user cannot click on
feature objects and see the flow in or out of that object.
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GMS supports SFR parameters.